This proposal seeks to develop a new class of light-responsive inorganic materials as chemotherapeutic agents. Cisplatin and its analogues remain the standard therapy for a variety of cancers, despite their nonspecific mechanism of action with nucleic acids, resulting in general cytotoxicity and debilitating side-effects. A promising approach that will provide several key advantages is to combine the reactivity of metal- based drugs with the selectivity of photodynamic therapy (PDT) to increase the targeting of malignant tissues and reducing side-effects. We have recently shown that structural distortion can be utilized to promote photochemical reactions to create reactive ruthenium species that are strongly electrophilic and highly photo-toxic in cell based assays. We hypothesize that distortion can be used to control light-activated cytotoxicity for the creation of selective and potent chemotherapeutics. We propose a new class of ruthenium-based compounds that have a readily modifiable modular design to facilitate rapidly incorporation of key molecular components to efficiently develop materials exhibiting selectivity and controlled reactivity. Coordination chemistry will be used to generate a structurally diverse family of three-dimensional chiral ruthenium compounds in a self-assembled manner. The structural variations in the materials will be correlated to cytotoxic efficacy using high-throughput cell survival assays, and the most promising compounds will be assessed for Pharmacokinetic (PK) properties, Maximum Tolerated Dose (MTD) and efficacy in mouse xenograft models of lung cancer and melanoma. Mechanism of action studies will be used to define the currently unknown process of cell killing. In order to accomplish this aim, a novel chemical labeling strategy is proposed to facilitate imaging of the subcellular and potentially sub-organellar localization of active compounds using Electron Microscopy. If successfully validated, this approach could be extended to additional imaging applications in tissues. Alternative approaches utilize biotin-labeled ruthenium materials for target pull-down, with cellular targets identified through a process of gel electrophoresis, chromatography, and mass spectrometry. In vitro and in cell transcription and translation assays will support these findings. Cisplatin, the benchmark inorganic chemotherapeutic, will be used for comparison in all mechanism of action studies. The goal is to determine if the proposed ruthenium materials utilize the same biological target(s) as cisplatin, or may be directed to different functional targets via structural modification. Upon completion of these studies, we will have expanded our knowledge of the fundamental photochemistry of ruthenium complexes, developed potent and selective cytotoxic chemical entities, identified their mechanism of action, and developed a new tool for the imaging of small molecules in biological systems. 1